There are at least five principle ways that you can be discriminated against at work based on your pregnancy.
Only if the real reason is based on the illegal factors embodied in the federal or state discrimination laws, then you got some leverage to hold your employer accountable.
If you are dealing with harassment in the workplace, very important that you complain to your employer. Give them a chance to investigate your allegations of gender discrimination, or harassment based on your race, color, pregnancy, national origin – it doesn’t matter. The point is, that you have to give the employer, the company, the opportunity to fix it.
Being fired for stealing whether you are guilty or not, doesn’t matter because your employer can fire you for any reason. Your employer can fire you for crazy reasons, just not illegal ones.
The question is – there is negative information in your personnel file at your job, and your employer won’t let you review it, see it, add to it, change it – is that legal?